Perfect Dratini hatched... Then what?

If you have a rare candy bottleneck for Rayquaza/Dialga/Palkia then max this one out, if you don't have a rare candy bottleneck then fair enough, focus on the legendaries before dragonite.

If you're never going to max out the other Level 33+s, they will get outplayed by this 100% maxed later down the line anyway. You could trade them to a baby account if you have one/will make one, or to other players for something reasonably compelling.

I'd say max it, its a perfect dragonite. I maxed mine after hatching a perfect, never regretted it despite the dust it set me back. I wouldn't worry about the dust cost, right now its fairly easy to farm massive amounts of it (as a semi casual pace just walking it got around 100k last night). Theres not too many big legendaries that will be exceedingly relevant when it comes to the gen 4 legendary raid bosses aside from darkrai who itself is unreleased, and few raids these days demand only legendaries for solo/duo so nonlegendary substitutes work well in their place, though the legendaries as better (most of the time, hi electivire).

Dragons have seen a bit of a decline in usage as generalists via recent developments (and by recent, I mean like 3 months ago), and not even the almighty ray was immune to this, the effectiveness change made specialists a lot better, and the addition of meteor mash metagross as generalist gym clearer. With Palkia, latias and giratina done, and ray handled better by ice these days, a dragon specialist dragonite (and really Ray too) will likely only see usage against latios who may come back for a weekend soon, and possibly down the line if niantic decides they want to give us Origin forme giratina. After gen 4, there will be some new dragon targets in gen 5, but because of the time gap and potential additions by then, Im not going to make any assumptions beyond 'potentially great' for best counters to far unreleased pokemon.

Beyond usage, this is just a personal thing, but something feel others may understand. I maxed my perfect dratini a while back, and its just nice to see that perfect CP at the top of the list when scrolling through it, even when she's not in use.

If you dont feel you need to evolve it, i'd say no harm in holding onto it.

I would say evolve it up to a Dragonite, but don't power it up right now - there isn't much of a need for a Dragonite in the game right now.

When Niantic brings back the "Power up a Pokémon 5 Times" research task (or maybe it's still out there and I just haven't gotten it in months), then power up the Perfect Dragonite.

Doesn’t look like you need it, just max it out as a side project... It definitely deserves to be maxed out...

I've been wondering something similar with a perfect Dratini I caught, albeit at a much lower level. Other people have suggested evolving and powering it up whenever you pick up the "power up 5 times" task, which I might do with mine.